Iminodiacetic acid compounds are useful in various applications. Such compounds (particularly iminodiacetic acid and its salts) are, for example, widely used as raw materials for making pharmaceuticals, agricultural chemicals, and pesticides, and are particularly useful as raw materials for making N-(phosphonomethyl)glycine and its salts. N-(phosphonomethyl)glycine, known in the agricultural chemical industry as “glyphosate,” is described by Franz in U.S. Pat. No. 3,799,758. N-(phosphonomethyl)glycine and various salts thereof can be conveniently applied as a post-emergent herbicide in an aqueous formulation, and as a highly effective and commercially important broad-spectrum herbicide useful for killing or controlling the growth of a wide variety of plants, including germinating seeds, emerging seedlings, maturing and established woody and herbaceous vegetation, and aquatic plants. Widely known processes for making N-(phosphonomethyl)glycine and its salts from iminodiacetic acid compounds are disclosed in, for example, Franz, et al., Glyphosate: A Unique Global Herbicide (ACS Monograph 189, 1997) at pp. 233–62 (and references cited therein).
Many previously disclosed processes for making iminodiacetic acid compounds convert an intermediate amine compound having at least two identical groups. For example, in U.S. Pat. No. 5,627,125 (and references cited therein), Ebner et al. disclose making disodium iminodiacetate by dehydrogenating two hydroxyethyl groups of N,N-diethanolamine using a strong hydroxide base in the presence of a metallic catalyst. Micovic et al. (Journal of Serbian Chemical Society, 51, 435–39 (1986)), on the other hand, describe making iminodiacetonitrile (HN(CH2CN)2), and then hydrolyzing iminodiacetonitrile in acid to form iminodiacetic acid.
Iminodiacetic acid compounds also have been prepared using, for example, processes in which the two carboxymethyl groups are introduced simultaneously. Jasik et al. (Pol. Organika, 1–8 (1986)), for example, disclose making iminodiacetic acid and its salts by reacting ammonia with about two equivalents of chloroacetic acid.
Iminodiacetic acid compounds additionally have been made through unsymmetrical chemical intermediates. For example, Sano et al. (Japanese Patent No. 46040611) disclose making iminodiacetic acid and its disodium salt by hydrolyzing N-cyanomethylglycine. Sano et al. report making the N-cyanomethylglycine by reacting glycine with glycolonitrile. Nakao et al. (Japanese Patent No. 55007252) likewise disclose making iminodiacetic acid and its disodium salt by hydrolyzing N-cyanomethylglycine, but Nakao et al. report making the N-cyanomethylglycine by reacting glycine with formaldehyde and an alkali metal cyanide. Sodium glycinate, from which glycine can be obtained readily, may be prepared, for example, by dehydrogenating monoethanolamine. See, e., Franczyk et al., U.S. Pat. No. 5,739,390.
A process for making iminodiacetic acid or a salt thereof directly from monoethanolamine substrate is highly desirable. Because mono-, di-, and tri-ethanolamines are all obtained when ammonia is reacted with ethylene oxide in the major commercial production process, monoethanolamine is now more readily available due to the large quantities of diethanolamine utilized commercially to produce disodium iminodiacetate and other materials. Use of monoethanolamine in a process involving a single cyanomethylation to make disodium iminodiacetate would substantially reduce the amount of the highly toxic hydrogen cyanide needed compared to bis-cyanomethylation of ammonia to produce disodium iminodiacetate. Availability of a viable alternative to the current commercial routes could further offer flexibility in the use of existing manufacturing facilities.
Applicants are not aware of any reported processes that directly utilize monoethanolamine to make iminodiacetic acid or salts thereof. Cyanomethylation of monoethanolamine has been disclosed by Athey et al. in PCT application publication number WO 9721669 and Ulrich et al. in U.S. Pat. No. 1,972,465. Chemically, N-cyanomethyl substituted amines are generally unstable, which make their reactivity difficult to predict for new types of reactions or when reactive substituents are present. Athey et al. and Kern (U.S. Pat. No. 2,169,736) report that N-(2-hydroxyethyl)glycine may be formed by alkaline hydrolysis of N-cyanomethylethanolamine in an unreported yield without mentioning any stability problems. Applicants are not, however, aware of any previously reported processes which simultaneously or sequentially convert the cyanomethyl group and the hydroxyethyl group of N-cyanomethylated monoethanolamines to form iminodiacetic compounds.